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-The Project Gutenberg EBook of The Geology of Groton State Forest, by 
-Robert A. Christman
-
-This eBook is for the use of anyone anywhere in the United States and most
-other parts of the world at no cost and with almost no restrictions
-whatsoever.  You may copy it, give it away or re-use it under the terms of
-the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org.  If you are not located in the United States, you'll have
-to check the laws of the country where you are located before using this ebook.
-
-Title: The Geology of Groton State Forest
-
-Author: Robert A. Christman
-
-Release Date: November 16, 2019 [EBook #60710]
-
-Language: English
-
-Character set encoding: ISO-8859-1
-
-*** START OF THIS PROJECT GUTENBERG EBOOK THE GEOLOGY OF GROTON STATE FOREST ***
-
-
-
-
-Produced by Stephen Hutcheson, Lisa Corcoran and the Online
-Distributed Proofreading Team at http://www.pgdp.net
-
-
-
-
-
-
-    [Illustration: Cover: Looking southward along Groton Pond from near
-    Stillwater Brook.]
-
-
-
-
-                             THE GEOLOGY OF
-                          GROTON STATE FOREST
-
-
-                                  _By_
-                          ROBERT A. CHRISTMAN
-
-
-                    DEPARTMENT OF FORESTS AND PARKS
-                      Perry H. Merrill, _Director_
-
-                     VERMONT DEVELOPMENT COMMISSION
-
-                       VERMONT GEOLOGICAL SURVEY
-                   Charles G. Doll, _State Geologist_
-
-
-                                  1956
-
-
-
-
-                     GEOLOGY OF GROTON STATE FOREST
-
-
-                                  _By_
-                          ROBERT A. CHRISTMAN
-
-
-
-
-                              INTRODUCTION
-
-
-Geology is the study of the history of the earth as recorded in its
-rocks. This study explains why certain types of rocks and minerals occur
-at one place and not another, why the forms of the land differ from one
-region to another, and why particular animal and plant remains are
-sometimes preserved as fossils in certain kinds of rocks. The
-professional geologist makes these studies his business; the amateur
-finds these studies a fascinating hobby; but the uninitiated person
-misses much of the pleasure of travel. Anyone who notices the difference
-between rocks or terrains and wonders "why?", has a potential for
-geology. Many fall into this class and it is for them that this booklet
-has been written. It is hoped that with its aid, the traveler or
-vacationer may come to know something about the geology of Groton State
-Forest. The author is confident that those who come into the habit of
-observing nature and the world around them will find more meaning in
-life itself. In any case, those traveling with children may find answers
-to some of their questions about minerals, rocks and mountains.
-
-Groton State Forest is not a geologist's paradise--as compared to
-Yellowstone Park or the Grand Canyon--but it does contain interesting
-rocks and land forms which can be explained geologically. In keeping
-with the calm, subdued and mature atmosphere of the Vermont countryside,
-the geology is unobtrusive. There are few jutting cliffs or bare rock
-exposures; all is mantled with vegetation. If this vegetation could be
-stripped away--admittedly, a postulation that would destroy the
-wilderness and charm that belongs to Groton--boulders and gravelly
-glacial deposits would be seen to fill the valleys. If in turn these
-boulders and the soil could be stripped away, a continuous floor of rock
-would be exposed. This would be a geologist's paradise--square miles of
-bare rock would be available for study. However, lacking the magic wand
-to perform this feat, we must be satisfied to glean what information we
-can from the existing rock exposures.
-
-To use a pun, it can be said that almost all the rocks found at Groton
-State Forest can be taken for granite. As well as has been determined,
-all the underlying rock is _granite_[1] and most of the boulders
-deposited by glaciers of the last ice age are the same type of granite.
-To avoid confusion in describing these rocks, the discussion has been
-divided into two parts: the first deals with the granite of the bedrock,
-and the second deals with the glaciation of the area and the deposits
-resulting from it. A third section describes the geology in some of the
-nearby areas.
-
-
-
-
-                       GRANITE AND RELATED ROCKS
-
-
-_Occurrence of the granite_
-
-Ledges of light-colored granite occur at the summits of most of the
-mountains and hills in the State Forest area and are found occasionally
-at lower elevations. They are conspicuous on Owlshead, Silver Ledge,
-Little Deer, Big Deer, Niggerhead and Spicer Mountains; smaller ledges
-also occur on Kettle, and Little Spruce mountains, Hardwood Ridge and
-the low hills east of Groton Pond. At lower elevations, granite is found
-at the outlet of Groton Pond, along the railroad tracks west of Groton
-Pond and at Stillwater Brook, along Osmore brook and at several other
-minor locations. These locations are shown diagrammatically on the map
-by a black dot. These dots indicate where the granite occurs but nothing
-about the extent of the exposure. If every location of exposed rock were
-marked with a dot, certain parts of the map, for instance, the west side
-of Niggerhead, would be solid black and the contour lines which show the
-elevation would be obscured completely.
-
-All these rocks are presumably part of one large mass of granite which
-extends deep below the surface of the earth. Most of this body of
-granite is hidden by the soil and bouldery glacial deposits, so that its
-exact areal extent is not known. It appears likely that it extends to
-the southwest to the vicinity of East Barre.
-
-
-_Description of the granite_
-
-The granite found at Groton State Forest is a gray to white,
-medium-grained rock with the mineral grains all about the same size.
-Surfaces exposed to weathering are generally darker in color and
-frequently are covered with scales of dark colored lichen. If the rock
-is broken to reveal an unaltered surface close examination will disclose
-individual mineral grains of mica, feldspar and quartz. _Mica_ occurs as
-very small plates which appear either white or colorless, called
-_muscovite_, or as black shiny plates called _biotite_. The _feldspar_,
-which is the most abundant mineral in the granite, has a chalky white
-appearance and may occur as tabular grains which reflect light from
-their flat surfaces when held in the proper position. _Quartz_, which
-contains only silicon and oxygen, the two most common elements in the
-earth's crust, is a transparent, glassy mineral which has no flat
-surfaces. It may appear gray because one can look down into the glassy
-mineral where there is no light source.
-
-A specimen of granite from Owlshead was studied with a microscope after
-it had been cut and ground to a thickness of only 0.03 millimeters. Many
-minerals, which ordinarily appear to be opaque, are transparent when
-ground this thin. By their various optical properties, the different
-minerals can be identified and the composition of the rock can be
-determined. Figure 1 shows a photograph, taken through a microscope, of
-one of these thin sections of granite. By careful examination of the
-thin section and by measuring the areal extent of the different minerals
-present, the rock was determined to contain, by volume, 35 percent
-quartz, 60 percent feldspar (in proportions of 25 percent _microcline_
-feldspar, KAlSi_3O_8 and 35 percent _plagioclase_ feldspar, NaAlSi_3O_8)
-and 5 percent mica (in proportions of 4 percent biotite and 1 percent
-muscovite). Although it is a member of the granite family, this rock
-should, in strict terminology, be called a quartz monzonite rather than
-a granite to indicate more precisely the mineral composition. Because of
-slight differences in composition, granite from the same body may
-elsewhere be correctly called granodiorite, quartz diorite or granite
-proper, depending on the relative amounts of the two feldspars and
-quartz. In this report these close distinctions have not been made and
-the rock is simply called granite.
-
-
-_Cracks in the granite_
-
-Two kinds of natural breaks, or cracks, occur in the granite in the
-State Forest area. _Joints_ are breaks which occur along plane surfaces
-and _exfoliation_ is the name given to the breakage along curved
-surfaces related to the exposure of the rock. Granite, as contrasted
-with other rocks, is characterized by its uniformity of texture and
-massiveness, so that any cracks present are conspicuous.
-
-    [Illustration: Figure 1. Photomicrograph of a thin section of
-    granite from Owlshead Mountain. The mineral with the grid pattern
-    (upper left) is a feldspar named microcline which has the
-    composition of KAlSi_3O_8. The one with the indistinct striped
-    pattern (lower center) is a feldspar named plagioclase, variety
-    oligoclase, which has the composition of approximately NaAlSi_3O_8.
-    The patterns for these minerals result from different portions of
-    the same mineral grain having different orientations, called
-    twinning, so as to give a different optical appearance. The clear
-    white mineral (right center) is quartz. The dark gray mineral with
-    the fine lines (upper center) is biotite and the smaller,
-    lighter-colored, elongate mineral to the right of the biotite is
-    muscovite. The other minerals are feldspar and quartz in different
-    orientations. The actual diameter of the clear white quartz grain
-    (right center) is about four-tenths of a millimeter so that the
-    photograph is a magnification of about one hundred.]
-
-Joints are more conspicuous of the two types, and typically belong to a
-general system so that at a given location they tend to be parallel. On
-top of Owlshead, for example, the most prominent joints trend N.25°W.
-(read: North twenty-five degrees to the west) with dips[2] that are
-vertical or dipping steeply to the southwest. Another set of joints
-trends N.10°E. with dips that are vertical or dipping steeply to the
-southwest. Joints represent the breakage of the rock due to stress and
-strain. Some joints result from tensional forces set up within the rock
-itself by contraction due to cooling of the originally hot solidified
-rock. Other joints result from larger-scale forces within the earth's
-crust which cause earthquakes and general movement of land masses. An
-exhaustive study of all the rocks in a large area would be required to
-determine conclusively the origin of the joints on Owlshead.
-
-In addition to the nearly vertical joints, a third set of nearly
-horizontal joints may be observed on cliffs. These joints are called
-_sheeting_ and apparently are related to the depth from a former
-topographic surface which existed at the time the sheeting originated.
-The vertical joints and sheeting are important qualities of a rock to be
-considered in choosing a rock for commercial quarrying. Not only do
-these factors effect the ease of quarrying, but they also determine the
-amount of waste material which would have to be removed and discarded
-because of poor size and shape.
-
-Exfoliation is the term for breakage due to the disintegration caused by
-decomposition of the rock on surfaces exposed to the weather. It is
-characterized by the scaling off of concentric shells of altered rock to
-produce a convex surface. Rocks showing exfoliation surfaces are not
-common at Groton. One of the best developed exfoliation surfaces,
-illustrated in Figure 2, occurs at the base of the cliffs on the south
-side of Owlshead Mountain.
-
-Once joints have formed, they are enlarged by weathering. In particular,
-rocks are pushed apart by a "frost wedging." When water freezes it
-expands by about one-tenth of its volume. If it is confined it may exert
-a pressure of as much as 138 tons per square foot. In this manner, huge
-blocks may be pushed apart. If they are at the edge of a cliff, or part
-of the cliff itself, they may eventually break off and fall to the slope
-below. The accumulation of broken rock at the base of a cliff is called
-_talus_.
-
-
-_Origin and age of the granite_
-
-The granite originated in the interior of the earth many million years
-ago as a molten mass, called _magma_. This magma moved upward through
-the earth's crust by a process of melting the pre-existing rock or by
-forcefully pushing it aside. When it reached its present position it
-became cooler and minerals began to crystallize out. However, as is
-shown in Figure 3, it is important to understand that the surface of the
-land was not in its present position and that the magma actually cooled
-beneath a considerable thickness of other rocks. These overlying rocks,
-now gone, acted as an insulator and prevented the magma from cooling too
-quickly. If the magma had risen through these rocks and reached their
-upper surface, it would have formed a lava flow similar to those of
-present-day volcanoes and would have cooled much more rapidly. Rocks
-formed near the surface are characterized either by being fine-grained
-without visible crystals or by having a few large crystals in a
-fine-grained matrix; they never have a uniformly,
-medium-to-coarse-grained texture. Thus, the texture of the granite at
-Groton State Forest proves that it cooled slowly and indicates that, at
-the time of cooling, the granite was not at the surface. This is a
-reasonable postulation because studies of the regional geology indicate
-that a large amount of rock has been removed from this area by erosion
-through the long periods of geologic time.
-
-    [Illustration: Figure 2. Exfoliation surface on the south side of
-    Owlshead Mountain. Joints, of the sheeting type, are visible in the
-    granite cliff. The decomposition of the granite by weathering in the
-    niches has resulted in small patches of soil. The boy in the upper
-    right gives the scale.]
-
-    [Illustration: Figure 3. Sequence of events at Groton State Forest
-    shown diagrammatically.]
-
-    [Illustration: A. The Waits River Formation and other younger
-    formations are deposited from a shallow sea during Ordovician time.]
-
-  YOUNGER FORMATIONS
-  WAITS RIVER FORMATION
-
-    [Illustration: B. The sedimentary rocks are folded and metamorphosed
-    and the granite is intruded into the older rocks and crystallizes
-    during Devonian time.]
-
-  WAITS RIVER FORMATION
-  GRANITE
-
-    [Illustration: C. Erosion removes much of the rock from the area.]
-
-  GRANITE
-
-    [Illustration: D. During the ice age, continental glaciers move over
-    the land and erosion by the ice forms Owlshead Mountain and the
-    basin for Groton Pond.]
-
-  ICE
-  GRANITE
-
-    [Illustration: E. Present topography, exaggerated.]
-
-  OWLSHEAD MOUNTAIN
-  RICKER MILLS
-
-Evidence that the granite was emplaced into the older rocks of the
-earth's crust can be seen at certain locations outside of the State
-Forest. At Ricker Mills, for example, narrow bodies of granite can be
-seen cross cutting the older rocks. A fuller description of the geology
-at Ricker Mills is given in a later section of this report. Another type
-of evidence showing that the granite came into older rocks is found in
-the occurrence of fragments of older rock incorporated into the granite.
-These are called _inclusions_ and represent broken pieces of older rock
-which were enveloped by the granite. Inclusions are like peach slices in
-jello in that the surrounding material solidified after they were
-dropped in. Inclusions were observed in rocks on top of Kettle and Jerry
-Lund Mountains.
-
-Near the covered picnic shelter at Ricker Pond, one of the large granite
-boulders deposited by the glacier contains inclusions. Although this
-boulder has been moved from its original occurrence, it probably has not
-moved far as it is composed of the white granite which is typical of the
-area. It is cut by several pegmatitic dikes. The most interesting
-feature is the occurrence of inclusions of elongate, layered bands of
-older rocks of gray to dark gray _schist_.[3] These relations are shown
-in the sketch of this boulder in Figure 4. A careful examination of the
-schist inclusions reveals that they contain small plates of biotite in a
-fine matrix of quartz and more mica. The contact between the schist and
-granite is gradational at places because when the rock was formed the
-hot molten granite was in the process of melting the solid schist. The
-schist resembles the rock which occurred in this area before the granite
-was intruded and which occurs in nearby areas where no granite is
-exposed. Older rocks of somewhat similar appearance can be seen at
-Ricker Mills and on top of Jerry Lund Mountain.
-
-The composition of the granite at Groton State Forest is nearly the same
-as that which occurs throughout this region of Vermont. Incomplete
-mapping suggests that the granite at Groton is part of a large mass
-which extends to the southwest to the vicinity of East Barre.
-Undoubtedly all the granitic rocks of this region are related although
-they are not continuous at the surface. They were all emplaced at about
-the same time following a mountain-building episode in which the older
-rocks were folded and metamorphosed. On the geologic time scale, the
-granites were emplaced near the end of the Devonian period which is
-estimated to be more than 300 million years ago.
-
-    [Illustration: Figure 4. Sketch of boulder of granite containing
-    pegmatite band and schist inclusions at picnic area at Ricker Pond.]
-
-  GRANITE
-  PEGMATITE
-  SCHIST
-
-
-_Aplite and pegmatite_
-
-Two other types of igneous rocks called aplite and pegmatite occur
-sparingly in Groton State Forest. Both of these are productions of
-crystallization of residual fluids or late stage magma related to the
-granite. These were emplaced along cracks or planes of weakness in the
-granite after the granite had solidified. When viewed from the surface
-the aplite or pegmatite generally appear as bands cutting through the
-granite. However, when the third-dimension is considered it is easily
-realized that they are tabular or sheet-like in shape. Igneous rock
-masses having these dimensions are called _dikes_. At Groton most of the
-dikes are nearly vertical with a thickness ranging from less than an
-inch to more than several feet and extending for considerable distances.
-On Owlshead, one of these dikes is nearly three feet thick. The extent
-of these dikes is not known because they are only partly exposed, in
-that they extend beyond the limited areas of rock exposure.
-
-    [Illustration:            GROTON STATE FOREST]
-
-    DREW MTN
-    NIGGERHEAD MTN
-    BLAKE HILL
-    NIGGERHEAD BROOK
-    KETTLE MTN
-    SPICER MTN
-    OWLSHEAD MTN
-    KETTLE POND
-    STILLWATER BK.
-    HARDWOOD RIDGE
-    BEAVER BROOK
-    SILVER LEDGE
-    LITTLE SPRUCE MTN
-    PEACHAM POND
-    DEER MTN
-    DEVIL'S HILL
-    PEACHAM BOG
-    LITTLE DEER MTN
-    OSMORE BK.
-    COLDWATER BK.
-    GROTON POND
-    JERRY LUND MTN
-    RICKER POND
-    RICKER MILLS
-  EXPLANATION
-    GRANITE EXPOSURES
-    SCHIST EXPOSURES
-    TRAIL
-    RAILROAD
-    SWAMPY AREAS
-    CONTOUR LINE WITH ELEVATION
-    CONTOUR INTERVAL IS 100 FEET
-      TOPOGRAPHY FROM U. S. GEOLOGICAL SURVEY MAPS
-      BY ROBERT CHRISTMAN
-
-The _pegmatite_ dikes are coarse-grained, in some cases consisting of
-individual mineral grains as much as two to four inches in diameter. The
-mineral composition of the pegmatites is nearly the same as the granite,
-except that biotite is usually absent. Because of their larger grain
-size, the minerals can be recognized more easily in pegmatites than in
-either granite or aplite. Quartz is glassy and breaks with smooth curved
-fractures. Feldspar is chalky white, or pink, and may occur as tabular
-crystals with straight-line contacts. It tends to break along definite
-intersecting planes which can be seen in their reflecting position.
-Muscovite occurs as "books" of semi-transparent leaves. The large
-"books" of muscovite are particularly interesting because of the
-fascinating fact that a mineral sheet can be split along a given planar
-direction into thinner and thinner sheets until they are too thin to
-handle. Theoretically the mineral might be split into sheets only as
-thick as one layer of atoms. The ability of a mineral to break along
-definite planes is related to its atomic structure and is called
-_cleavage_. The cleavage in mica is perfect, whereas the cleavage in
-feldspar is only poorly developed, and quartz does not possess cleavage
-at all.
-
-The _aplite_ dikes are composed of nearly the same minerals as granite
-except that the average grain size is smaller. They are characterized by
-the absence of dark minerals and muscovite and by a high quartz content
-which gives the rock a "sugary" appearance. Most of the aplite dikes are
-less than six inches thick.
-
-Inasmuch as the pegmatite and aplite dikes both cut through the granite,
-they both must be younger in age than the granite. As is shown by the
-relations between these two types on Owlshead (reproduced in Figure 5),
-the pegmatite dike is younger because it cuts across the aplite dike.
-This is the general age relationship for these dikes in this age.
-
-    [Illustration: Figure 5. Sketch showing aplite and pegmatite dikes
-    in the granite on Owlshead Mountain. The cross cutting relations
-    show that the pegmatite is youngest and that aplite is younger than
-    the granite but older than the pegmatite. In the distance is Kettle
-    Pond and Kettle Mountain.]
-
-  GRANITE
-  APLITE
-  PEGMATITE
-
-
-
-
-                               GLACIATION
-
-
-Although the causes of the ice ages remain a matter for conjecture, the
-fact is established that the northern part of North America was covered
-by a thick sheet of moving ice several different times beginning about a
-million years ago. As the effect of the last glaciation erased much of
-the evidence of previous glaciations, the present topography can be
-related to that last one. Rather accurate dating by measuring the
-radioactive decay of Carbon 14, indicates that the ice of the last
-glaciation retreated from the area about 12,000 years ago. Because the
-climates between the four glaciations were as warm, if not warmer, than
-our present-day climate, geologists have speculated that the world may
-now be in a warm period and that another ice age is scheduled to occur
-some time in the distant future.
-
-The effect of continental glaciation upon a land mass is twofold. First,
-the glaciation acts as an erosive agent which tends to scoop out the
-areas of softer rock and wear down the areas of more resistant rock.
-Secondly, when the glacier begins to melt, it drops large quantities of
-gravel and boulders which had become incorporated within the glacier.
-Most of this material is picked up by the glacier as it moves over the
-land; some falls onto the glacier where it occupies a valley. Some of
-the sand, gravel and boulder deposits left by the glacier are
-distinctive in form and composition and others are characterized by
-their complete lack of distinctive shapes, and the utterly chaotic
-nature of the material deposited. The deposits at Groton State Forest
-seem to be the latter type.
-
-
-_Erosion and deposition by the glacier_
-
-The shape of Spicer, Owlshead, Little Deer and Big Deer mountains are
-primarily the result of the erosive action of the glacier as it
-continually moved southward over the land for a great number of years
-during the last glaciation. When a continental glacier encounters a hill
-or mountain of resistant rock, it tends to scour the rock on the up-ice
-side of the hill and to "pluck out" the rocks on the leeward side. For
-this reason these mountains have broad gentle slopes on the side from
-which the glacier came and they drop off sharply on the side from which
-material was removed by plucking action. The last part of Figure 3
-illustrates how these mountains may have been formed. Such prominent
-rock exposures which have been subjected to glacial erosion originally
-showed deep scratches, called _glacial striae_, cut by cobbles dragged
-along the bottom of the glacier. Unfortunately, on most prominences in
-Groton State Forest exfoliation of the rock has erased these markings;
-but it is possible that striae may be found on recently uncovered rock
-exposures.
-
-The depressions in which Groton and Osmore ponds are located probably
-represent areas in which the glacier scooped out material to a greater
-depth than elsewhere either because of channeling of bottom flow between
-topographically prominent features, or because of subtle differences in
-rock hardness.
-
-When the glacier retreated, that is when it was melting faster than it
-was advancing, it dropped material in a helter-skelter manner. _End
-moraines_, which are ridges of gravel formed where the front of the
-glacier was stationary because of a close balance between rates of
-movement and melting, are not evident in Groton State Forest. As far as
-can be determined, the material was deposited irregularly over the
-entire area, so that boulders dropped by the glacier are found
-everywhere. These are particularly noticeable around the lakes where the
-fine material has been removed and the soil and forest cover does not
-hide the boulders.
-
-Almost all of the boulders deposited by the glacier are composed of
-white granite similar to the rock which underlies the entire area. This
-indicates that most of the boulders have not been transported very far.
-However, occasionally boulders are found which are not characteristic of
-the area and represent rocks brought in from the north. Such boulders
-which are foreign to the area in which they are found are called
-_erratics_. Most erratics in this area are dark-colored metamorphosed
-rocks in which the minerals are oriented to give the rock a layered
-pattern. These are called either _gneisses_ or _schists_ depending on
-whether the layering is coarse or fine. Deposits of the glacier are
-exposed in two gravel or sand pits near the Stillwater Camp site. These
-deposits are composed principally of sand but contain scattered boulders
-of different sizes. A few erratics are found in these
-deposits--particularly a variety of rock which weathers to a soft, brown
-porous mass resembling decayed wood. These sandy deposits probably were
-plastered onto the ground from the sole of the creeping glacier or were
-simply let down as the glacier wasted away.
-
-Because of the irregular manner in which the glacier may deposit its
-load of sand and gravel, the topography in such areas is uneven and
-characterized by poor drainage. At a number of places in Groton swampy
-areas occur at higher elevation which might normally be expected to be
-well-drained. Some of these areas have become the sites of beaver dams
-because they are ideal for damming up the water.
-
-
-
-
-                        GEOLOGY OF NEARBY AREAS
-
-
-_Ricker Mills_
-
-Just south of the park at Ricker Mills some of the oldest rocks in the
-area are exposed in the railroad cut just north of the highway crossing.
-These rocks belong to a thick sequence of similar rocks which are
-collectively called the _Waits River formation_. Studies in other areas
-indicate that these rocks belong to the portion of geologic time called
-the Ordovician period which was more than 350 million years ago.
-
-The Waits River formation represents a series of sediments which
-accumulated at the bottom of a shallow sea during Ordovician time. These
-sediments included both limy and sandy beds, and fossils may originally
-have been preserved in some of the beds. Sediments of other types later
-accumulated over the Waits River formation during a long period of
-geologic time, so that eventually the formation became deeply buried.
-(See Figure 3.) The sea retreated and the rocks were subjected to high
-pressure and temperatures during a period of mountain-building. The
-rocks which had been sedimentary were folded and converted to
-_metamorphic rocks_ by partial melting and recrystallization of the
-components. As a result the rocks became schists or marbles. Any fossils
-which may have been present were destroyed or badly altered in the
-process. This is unfortunate because valuable geologic information as
-the age of the rocks can be determined from the type of fossils present.
-
-The rocks of the Waits River formation at Ricker Mills are dominantly
-mica schists with layers containing limy material. These are too impure
-to be considered marble but enough lime is present so that they react
-strongly with acid, a test for detecting the presence of lime. The
-schists principally contain quartz, biotite, calcite (lime) with lesser
-amounts of muscovite, feldspar and impurities. The rocks weather to dark
-colors; the gray limy beds are particularly susceptible to weathering
-and turn dark brown to black on the surface. When more lime is present,
-the rock weathers to a deep brown porous rock which resembles decayed
-wood. Some boulders of these altered limestones are found in the glacial
-deposits in the State Forest.
-
-An additional factor which makes the rocks in the railroad cut at Ricker
-Mills look "messy" is the iron and manganese staining and the formation
-of mineral crusts on the surface of the rocks through the action of
-ground water. Rain water falling on the hills above passes through the
-soils, dissolving minerals, and precipitating them where the water seeps
-out and evaporates at the lower level of the railroad tracks.
-
-The schists trend about N.80°W. and dip about 30° to the northeast.
-Along the length of the rock exposures it can be seen that this dip is
-not constant but varies from 10 to 30°. The variation in dip gives the
-schists a wavy appearance.
-
-At two places along the railroad cut, the schist has been intruded by
-granite. As is shown in Figure 6, which is a sketch of the rocks exposed
-on the east side of the railroad, the granite forms vertical dikes. As
-the schist ends abruptly at the contact of the granite, this indicates
-that the granite formed after the schist. The granite is nearly the same
-as the granite in Groton State Forest except that the mica is muscovite
-rather than biotite. For this reason the granite is lighter in color on
-fresh surfaces. In general the exterior is dark in color due to the
-staining of iron from weathering of the mineral pyrite, an iron sulfide,
-which occurs in small amounts in the granite.
-
-
-_Jerry Lund Mountain_
-
-On top of Jerry Lund Mountain occur other outcrops of the Waits River
-formation and granite. Their exact relationships cannot be seen easily
-because of the thick vegetation. The Waits River formation on Jerry Lund
-Mountain is composed principally of quartz mica schist.
-
-
-
-
-                             TRIPS TO TAKE
-
-
-_Hiking in the State Forest_
-
-The hike from the end of the road to the top of Owlshead Mountain takes
-only ten to fifteen minutes. A splendid view of the surrounding area,
-particularly Groton and Kettle ponds, is obtained from here. If
-possible, everyone who visits the park should take this short walk. The
-granite is well-exposed at the summit and dikes of aplite and pegmatite
-may be seen.
-
-The more venturesome park visitor will want to make other trips away
-from the "beaten path" into the wilderness of the Vermont woods. The
-principal difficulty arises in that the wilderness is so real a person
-may well become lost if he strays too far from the trails. Some of the
-trails have become overgrown so that they are difficult to follow and
-portions of others have been destroyed by the damming up of brooks by
-the beavers. It is suggested that in planning hikes information be
-obtained from the park superintendent about the condition of the various
-trails.
-
-    [Illustration: Figure 6. Diagrammatic sketch showing the relations
-    between the schist of the Waits River formation and the granite on
-    the east side of the railroad cut, at Ricker Mills.]
-
-  GRANITE
-  WAITS RIVER FORMATION
-
-An interesting hike can be made from Osmore Pond to Deer Mountain but as
-the trail is poorly marked, one must maintain a sense of direction. From
-the Osmore picnic area walk south near the shore of the pond to its
-outlet into Osmore Brook. At this point turn left to the northeast and
-follow the trail which parallels a wire marking the edge of the game
-preserve. About three-fourths of a mile from Osmore Brook the trail
-meets another trail at right angles. To the left the trail follows the
-game preserve boundary northwestward. The trail to the right leads
-directly to the top of Deer Mountain where a view may be obtained on the
-south side of the summit. As an alternate route for returning, follow
-the trail along the game preserve to the northwest. Some distance beyond
-a shelter-lean-to the trail divides several times with the main trail
-leading to Blake Hill and other trails to the left leading to the Osmore
-Pond road.
-
-A hike along the trail on the north side of Kettle Pond to the
-shelter-lean-tos makes a pleasant trip along the water. Also, the trail
-from Owlshead Mountain to Osmore Pond is convenient for a short hike
-through the woods, if the trail can be found.
-
-
-_Quarries at East Barre_
-
-The granite quarries at East Barre are in nearly the same type of rock
-as that which occurs at Groton State Forest. The quarry operations are
-interesting and educational and the quarries afford a good opportunity
-of seeing fresh, unaltered specimens of granite. Guide service is
-offered at some of the quarries.
-
-
-
-
-                               FOOTNOTES
-
-
-[1]_Granite_ is a type of igneous rock consisting of large interlocking
-    grains of light-colored minerals. Rocks are classified as being
-    either igneous, sedimentary, or metamorphic. _Igneous_ rocks form by
-    the solidification of molten material; _sedimentary_ rocks form by
-    the accumulation of sediments derived from older rocks; and
-    _metamorphic_ rocks form by the recrystallization of older rocks
-    under conditions of high temperatures and pressures.
-
-[2]_Dip_ is the inclination of a surface as, for example, a joint
-    surface described above.
-
-[3]_Schist_ is the name given to rocks in which the minerals have a
-    parallel alignment due to reorganization of the rock constituents
-    during a condition of high temperature and pressure. The platy
-    minerals, like mica, form at right angles to the pressure so that
-    the resulting rock may have a "bedded" appearance.
-
-
-    [Illustration: Looking northwest over Groton Pond toward Owlshead
-    Mountain]
-
-    [Illustration: Looking north over Groton Pond toward Little Deer
-    Mountain]
-
-
-
-
-                          Transcriber's Notes
-
-
---Silently corrected a few typos.
-
---Retained publication information from the printed edition: this eBook
-  is public-domain in the country of publication.
-
---In the text versions only, text in italics is delimited by
-  _underscores_.
-
-
-
-
-
-
-
-End of the Project Gutenberg EBook of The Geology of Groton State Forest, by 
-Robert A. Christman
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